1. Field of the Invention
This invention relates to shock absorbers for linearly decelerating a machine part by imposing a relatively constant force to the part over the stroke of the device and more particularly to such a device wherein the constant decelerating force may be adjusted for use with machine parts having differing weights and velocities.
2. Prior Art
Shock absorbers which force fluid through a restricted orifice to convert the kinetic energy of a moving part into an increase in the thermal energy of the fluid are commonly used on machines. The smoothest deceleration of the moving part is obtained by absorbers which offer a constant resistive force to the motion over the total length of the deceleration.
One class of such devices employ a piston connected to the machine part and movable within a cylinder having one closed end. A series of exponentially spaced holes are formed along the length of the cylinder wall and the cylinder is supported within a housing filled with fluid. As the piston is forced into the cylinder by motion of the machine part the fluid is forced through the orifices and the kinetic energy of the part is converted into thermal energy of the fluid. As the piston moves down the cylinder it successively closes off the orifices so that the force imposed on the load is maintained relatively constant resulting in a linear deceleration of the moving part.
The force imposed on the part is a function of the configuration of the fluid orifices, and linear decelerators of this class have been designed wherein the orifice configuration may be varied to accommodate the device for use with parts having varying weight and kinetic energy. One approach to this problem has been to place a tubular sleeve over the cylinder and provide ports in the sleeve that cooperate with the ports in the cylinder to define the fluid orifice. The angular position of the sleeve on the cylinder may thus be adjusted to vary the orifice configuration and the resistance provided to a load. For example, Gryglas U.S. Pat. No. 3,425,522 discloses a hydraulic shock absorber employing a sleeve with a crescent-shaped groove that overlies a metering port in the cylinder.
The present invention is directed to a fluid shock absorber of this general type, but which is provided with a unique orifice arrangement that is advantageous over prior art devices in two important respects. First, the orifice is configured to have a high ratio of width to length in order to maximize turbulent flow through the orifice and thereby minimize the sensitivity of the force required to push the fluid through the orifice to variations in the viscosity of the fluid. Second, the orifice is configured to also have a small area relative to the cross-sectional area of the groove measured at any point along the inner diameter of the tubular sleeve so as to cause a substantial pressure drop when the fluid flows through the orifice into the groove. By lowering the pressure in the groove, the likelihood of fluid leakage between the sleeve and cylinder is minimized.
The shock absorber construction is also such as to greatly simplify the assembly of the unit and to eliminate the possibility of the parts being assembled in incorrect relation.